Air propeller



Dec. 27, 1949 R J, REEKv 2,492,653

AIR PROPELLER Filed April l1. 1946 2 Sheets-Sheet l j l n 4:. INVEVI'OR. @Y 71%' pff/f BY (M 3 @Lw-11A Patented Dec. 27, 1949 UNITED STATES PATENT OFFICE AIB' PROPEEILEBT Application April 11 4l Claims,

invention relates to propellers, and more particularlyV to air propellersY of the type in which the blades are arranged to be rotated about their axes; in response to changing conditions of operation, such as number of revolutions of the propeller..

The present invention comprehends the provision of a variable pitch air propeller having a. ne pitch. setting in which it is held by the summation of the moments acting in a pitchdecreasing direction, and a coarse pitch setting into which it is moved by the summation of moments acting in a pitch increasing direction.

It". is an object of the invention to provide a variable pitch air propeller in which the cen-v trifugal force` of the propeller blades eifect ay change in blade pitch setting.

A further object of the invention lies in the provisionv off a variable pitch air propeller constructed and arranged so that its blades are normally in fine pitch position, but responsiveA tothe centrifugal force of the blades above a predeterminedvalue to cause the blades to shift to coarse` pitch position with a snap action.

Av still furtherobject of the invention resides in the provision of a variable pitch air propeller movable from a normally fine pitch position to a coarse pitch position in response to the centrifugal forcev of the propeller blades acting through a ball nut assembly.

The above and other objects and features of theA invention will be apparent from the following description of thev apparatus taken in connection with the accompanying drawings which form a part of the specification, and in which:

Figure 1= is an elevational View of a propeller hub with portions broken away to show the internal mechanism;

Figure 2'is-a transverse section of the hub taken substantially on the line 2-2 of Figure 1, with the propeller show n in coarse pitch;

Figure 3 isV a transverse section of the hub Referring nowtoFigure 1 of'fthedrawings,` the;-

referenceA numeralv [r designates 'a propeller hub 1946;'SeriaLNo. @H3425 havingf a fiarlge I2l *which abuts a flange I4 carriedr by a propellerdrive shaft I6 driven by any engine, not shown. TheV flanges l2 and i4 are drilledy at: |582 to receivebolts to securely holdTv 30 are; received partly in each of the grooves 22 and24: to. provide a screw. and` nut assembly in which the hub may be considered the nut, andr theJ memberl 25" theI screw.` or ferrule. This arrangement provdes a relatively frictionless assembly whereby the propeller blades 28 may be rotated about their. axes. Tubes 3| provide return paths for the balls 30'. It should be noted 20,1that the number of' return tubesv is optional, de-

pendingl on. the requirements of the assembly.

The propeller blades are normally urged to fine pitch. setting-(see Figure 3) by a plunger 32r slidably. located' in. bore 34 ofthe propeller shaft I6. 25A spring 3B, having preselected characteristics, is disposedk within the bore 34 so that its free end acts on the plunger to normally bias the same` toi the right. The, plunger is provided with a stop element38 located exteriorly thereof so as to engagean` extension. MJ ofshaft I6 to limit the axial'. displacement of the plunger to thereby establish theA maximum coarse pitch of the propeller blades (see Figure. 2)-. The normal ne pitch setting of the blades is accomplished by constructing one-end ofthe plunger with an extension. 112l which abuts an adjustable plug 44 carried" by the. hub. This limits the axial displacementl of the plunger 32 in a direction establish-ingy the` minimum ne pitch setting of the blades. The plug 44 provides means ,for adjustlng the fine pitch setting'ofA the blades within a predeterminedlpitch range. To facilitate assemblyoffthe plunger 32 within the bore 34 a sleeve 48' is providedfwith a closed end portion 5! drilled at 52T to` receivel a bolt stud 54 which is screwthreaded into one end ofthe plunger. The end of the-.sleeve 48 oppositev from the closed end is constructed withI anl outwardly turned flange 56 which engages one-endl of the spring 36, the opposite or freeend of' which abuts the plunger. The plunger* 32', spring-36', sleeve 48 and bolt stud 541 comprise'an assembly which is held to.- gether by the boltstud 54* when removed from thebere 3.4:" -55. Tha-members finto which the ends of the propeller blades are iitted are equipped with integrally attached rollers ed. It should be noted that the rollers 53 are disposed outside of the axes of rotation of the blades to provide a lever for rotating the blades in a manner to be hereinafter described. rlhe plunger 32 has a cam B integral therewith and on which the rollers 58 ride. The cam Sil, of Figures 1 vto 4, and 6a has two cam .faces e2 and 6d. The profile of the cam is determined by the requirements of the propeller blade pitch regulation. The instant cam is for a two-position propeller having iineand coarse pitch positions only with pitch positions. l

The arrangement of the mechanism -is such that the centrifugal force of the propeller blades is resolved into a pitch increasing moment through the ball nut assembly. That is, the axial or centrifugal force of the propeller blades is converted into a torsional or twisting force which causes the blades to rotate about their axes in a pitch increasing direction. Also the aerodynamic forces acting on the propeller blades are' in a pitch increasing direction. These latter forces are comparatively small and need not be considered in the present discussion.

Opposing these pitch increasing moments are pitch decreasing mo-ments. The spring urged plunger and cam assembly provide a part of the pitch decreasing moment.v In the instant case the blades are so arranged that the centrifugal twisting moment of the bladesl acts in a direction of pitch decreasing moment at all times to supplement the spring force.

In moving the propeller blades from a fine pitch position to a coarse pitch position it will be noted that the shift is against' the spring loaded plunger 32 through the cam Eil.'

The spring 35 normally holds the propellerv blades in a predetermined line pitch position, as shown in Figure 3. In the case of the twoposition cam the blades are always balanced in both positions. A predetermined definite force is necessary to cause the blades to be shifted from one position to the other. There is no range of blade pitch between fine and coarse pitch in the case of the two-position cam.

Figure 3 shows the propeller blade in a predetermined ne pitch position with the roller 58 riding on the cam surface 52. The layout of the cam surface 52 is such that the blades will remain in ne pitch until a predetermined propeller speed is attained, at which time the blades will be shifted to coarse pitch. That is, the rollers 53 will shift from cam surface 52 to cam surface Eil. In coarse pitch the rollers 58 ride on the cam surface 54 which is constructed to provide an increased mechanical advantage. This increase in mechanical advantage, due to the difference in cam profiles allows a decrease in propeller speed within predetermined limits during the coarse pitch position and also makes available additional energy which is utilized to shift the propeller blades to coarse pitch. with a snap action. Also, when in coarse pitch if the speed of the propeller blades falls below a predetermined value, the blades will be automatically shifted back to ne pitch position.

Action of the automatic two-position control can be best shown by reference to Figure 6. The ordinate of the graph represents degrees in propeller pitch displacement and the abscissa is laid oiT in inch-pounds. The pitch increasing moments being positive above the line a-b, and the pitch decreasing moments being represented by a negative force below the line a-b. The pitch decreasing moments are shown as negative quantities since the summation of the pitch decreasing moments act in a direction to oppose the summation of the pitch increasing moments. Curves A and B represent the summation of the moments acting in a pitch decreasing direction at propeller speeds of 2000 and 2500 R. P. M. respectively. As indicated in the graph, with the blades in ne pitch position, it requires a pitch increasing force in excess of 158i) inch-pounds rotate the propeller blades about their axes no intermediate to thereby shift the blades to increase the blade pitch. At 2560 R. P. M. (see curve C) of the propeller blades the summation of the moments acting in a pitch increasing direction eXceed the summation oi the moments acting in a pitch Adecreasing direction to produce the aforemenshift the blades from line to coarse pitch at 250i) R. P. M. with the rollers 53 on surface E2 is somewhat less than the energy available for completingr the shift of the blades from fine to coarse pitch after the rollers 58 have been moved onto the cam surface 64 because of the increase in mechanical advantage. It will be noted, with reference to Figure 6, that the summation of the moments acting in a pitch decreasing direction diminish as the pitch tends to increase thereby increasing the unbalanced effect until the blades are urged into a coarse pitch position. After the shift of the blades to coarse pitch if the speed of the blades is reduced to 2,000 R. P. M. (see curve F), the summation of the pitch. decreasing moments become greater than the summation of the pitch increasing mo7 ments to thereby cause the blades to resume fine pitch. The energy available for shifting the blades from coarse pitch to ine pitch position is shown by the shaded area between curves F and A.

Figure 5 shows an alternative form of cam 'i0 adapted to be used for maintaining a substantially constant speed oi the engine with automatic selection ci governed speed. The cam 1!) comprises two cam faces 'l2 and l on which the rollers 58 ride. The action of the pitch increasing and pitch decreasing moments on the propeller blades where the cam lll is used can be best vshown in Figure 7. lll/'ith reference to Figure 7, the ordinate represents degrees in propeller pitch displacement and the abscissa represents force in inch-pounds. The pitch increasing m0- ments being considered positive above line c-d and the pitch decreasing moments being considered negativo below e-d. Curve H represents the summation of the moments acting in a pitch decreasing direction. Curve K represents the summation of the moments acting in a pitch increasing direction at 25il0 R. P. M. of the propeller. It should be noted that point P corresponds to the minimum fine pitch setting of the propellerblades. The blades are normally held in a predetermined nne pitch setting by the summation of the moments acting in a pitch decreasing direction. Curve T represents the summation of the moments acting in a pitch increasing direction at 2300 R. P. M. of the propeller. With this setting of the blades in'ne pitch position the rollers 58 weiilbeeina'diposition in Figi-1re at P' onlcam face 12. Whenthe propeller.

thi?.-l Ineclianical* advantage and.- to,- further-shift.,

the. biadesii a pitch increasing. directiom. whichL action tends to produce a reduction in the speed of the engine becausefof the-:increased load on the propeller. Of coursemmfnnther tendencyr tof increase. engine or propeller.V speedy will cause a further shit of' S' along camsuriace 14. inra pitch, increasing direction so as, to. put atgreater load" on the propeller blades. Obviously, with the cam arrangement of Figure 5 there are an innite number of blade settings available for take-olf and cruising. In the take-off pitch range, for example, there are an infinite number of blade settings available along cam surface 12 to maintain a speed of substantially 2500 R. P. M. When it is desired to cruise, the R. P. M. of the propeller is iirst caused to be increased above the 2500 R. P. M. so that the pitch increasing moments will become great enough to shift the rollers 58 onto the cam surface 14 and to increase the propeller blade pitch an amount which will load the blades to cause the R. P. M. to fall to substantially 2300 R. P. M., which has been selected as the cruising speed. In the cruising pitch range the saine as in the take-olf pitch range, there are an infinite number of blade pitch settings available to hold the propeller at substantially 2300 R. P. M.

Operation of the two-position device is as follows:

When the engine is idling, the summation of the moments acting in a pitch increasing direction is less than the summation of the moments acting in a pitch decreasing direction and the blades at this time are in fine pitch. During takeoff, the increased power applied to the propeller increases the speed thereof to a value determined by the forward speed of the aircraft. After the aircraft has reached a speed of approximately 80% of its maximum speed, the propeller R. P. M. will have increased to 2500 and the summation of the pitch increasing moments will exceed the summation of the pitch decreasing moments to thereby shift the blades in a pitch increasing direction, at which time the rollers 58 ride on cam surface 64 of cam 60.

During cruising, the propeller is maintained in coarse pitch. However, should it be desired to climb or if the engine is throttled to land the aircraft, the propeller R. P. M. is reduced below 2,000 R. P. M. and the propeller blades are moved to fine pitch position. That is, at this time the summation of the moments acting in a pitch increasing direction become less than the summation of the moments acting in a pitch decreasing direction and the blades shift to ne pitch.

Although this invention has been described in connection with certain specific embodiments, the

principles are susceptible of numerous other applications that will readily occur to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described the various features of tue-inventent. wheel-reame est new: ano. desirez 1i, airevoliiablezhubaf wttinhelinalfigrpomesifnrmedfimitsrends, bladesx diseposed-insthfrendgottherhinb;reuoluahleltherewitm and? rotatabek about: their axes; said; blades` have., ing; neli'cah groottes:1 at one; end; for -mating` withitheigroeves inzthesendsgofithehub, balls having.- pontipns: dispcsed partlyffim each: of?, the. mating; 'grooves` provide. a comparativetsev frictionlessassenrlzily: for' con-venting the centrifugaif: force. of? the revolving blades into a pitch increasingifmo men-tt' tending to! rotate the blades about their axes to increase the pitch thereof,v rollers car- ;ried by said oneerrdiofftheblades and mounted eccentric: te.- ,theI axes thereon. means;1 normally holding the blades in a predetermined fina pitch, position including a plunger having a cam thereon engaging the rollers, and a spring for urging said cam against said rollers, whereby rotation of the blades from said predetermined fine pitch position in response to propeller speed beyond a preselected value moves the plunger against the force of the spring.

2. An air propeller comprising a revolvable hub with helical grooves formed in its ends, blades disposed in the ends of the hub revolvable therewith and rotatable about their axes, said blades having helical grooves at one end for mating with the grooves in the ends of the hub, balls having portions disposed partly in each of the mating grooves to provide a comparatively frictionless assembly for converting the lcentrifugal force of the revolving blades into a pitch increasing moment tending to rotate the blades about their axes to increase the pitch thereof, rollers carried by said one end of the blades and mounted eccentric to the axes thereof, means normally holding the blades in a predetermined fine pitch position including a plunger having a cam thereon engaging the rollers, means urging said cam against said rollers, whereby rotation of said blades from said predetermined ne pitch position in response to propeller speed beyond a preselected value moves the plunger against said last named means, and adjustable means carried by the hub for varying the predetermined fine pitch position of the blades.

3. An air propeller for use on an aircraft comprising a revolvable hub, blades disposed in the hub revolvable therewith and rotatable about their axes, means in the hub for converting the centrifugal force of the revolving blades into a pitch increasing moment tending to rotate the blades about their axes to increase the pitch of the blades, means normally tending to rotate the blades about their axes in a direction opposing the pitch increasing moment, said last named means comprising a cam carried by the hub and movable relative thereto, said cam being formed with surfaces which provide speed range settings for take- Off and cruising, each range having an infinite number of predetermined blade pitch settings, `means engaging the surfaces of said cam and car.. ried by said blades, and means biasing said cam against said last named means.

4. An air propeller adapted to be driven by an engine and comprising a revolvable hub, blades having ends disposed in the hub revolvable therewith and rotatable about their axes, means in the hub for converting thecentrifugal for-ce of the revolving blades into a pitch increasing moment tending to rotate the blades about their axes to increase the pitch of the blades, means normally tending to rotate the blades about their axes in a direction opposing the pitch increasing moment including a member carried on the end of each blade and located eccentric to the blades axes, av 'cam movably mounted on the hub and formedwith a pair of profiles, one of which is for take-01T range and the other of which is for cruising range and against which proles said members abut to thereby position the blades for a constant engine speed in any one of the ranges, with automatic selection of governed speed for both ranges, and means biasing said cam against said members.

- ROYAL J. REEK.

REFERENCES, CITED The following references are of record in the file "of patent:

8 UNITED STATES PATENTS Number l5 Number France Jan. 17, 1936 

